This invention relates to heat sinks and especially to fasteners and nut assemblies use to attach or tie-down heat sinks to printed circuit boards and/or microelectronic circuit “chips”.
In assembling electronic components and modules, inserts, spacers and standoffs have been often used. The attachment of components and parts has been accomplished by screws, spring clips, clamps and other such devices. In a chassis for holding electronic components, space for the manual manipulation of parts, fasteners, and tools is often an issue.
Captive fasteners, such as captive screws and captive nuts are devices used to fasten two components/objects together, where the fastener remains with one of the components when loosened. Typically included with these fasteners is a tie-down spring which permits the alignment and other movement between the two fastened objects.
The captive fastener is “caught” to a component/object by a flange, a ferrule, a spring clip or the like. This retaining structure prevents the total removal of the captive fastener from that component.
Modern large scale integrated (LSI) circuits, microprocessors, microchips and other integrated circuit devices (IC chips) generate a substantial amount of heat, especially when operating at very high frequencies. Such heat generation can amount to 10's of watts and even 100's of watts of heat per hour. It has become imperative to mount heat sinks on these IC chips to dissipate as much heat as possible. In such instances the heat sink is mounted to the circuit board, or mounted to a mounting frame, which in turn is mounted to the circuit board on which the IC chip is also mounted.
Spring clips have been used to secure heat sinks, but are sensitive to vibration. They often interfere with the heat transfer fins on the heat sink and are often hard to positively snap into place and to release.
Captive fasteners have provided and improvement over heat sink clips. Two or four captive fasteners, such as screws or nuts, are used to engage respective flanged corners of a heat sink. These captive fasteners have threaded ends which usually engage a threaded ferrule or a threaded bushing, or a threaded screw/bolt mounted into a hole through the PC board.
Oftentimes a sheet of compressible elastomeric heat transfer polymeric material is used between the top surface of the IC chip and the bottom of the heat sink. This heat transfer interface material takes up for any surface irregularities in the mating IC chip and heat sink thereby providing the greatest positive surface contact.
Captive fasteners for IC chip heat sinks, with heat transfer polymeric sheeting, have incorporated spring tie-downs. The tie-down force exerted on the heat sink is the total of the spring forces of the compressed springs. This structure permits each heat sink to “float”, i.e., to move through expansion and contraction phases as the IC chip temperature changes.
The chassis (i.e., chip size) of microprocessor and electronic modules is becoming smaller with smaller footprints. As more boards are crowded into tightly spaced cases or into tightly spaced racks in a chassis, the size and position of heat sink tie-down screws, including captive fasteners, becomes an issue. The alignment of the heat sink during its mounting over an (integrated circuit) IC chip requires an ease of alignment of the captive fasteners with the board mounted receiving members (an easy operation in the alignment of the fasteners). This can require, generally, two hands and some lateral movement. This lateral movement can jeopardize the integrity of the printed circuit coating, and can create a missalignment of the interface polymer heat transfer pad on the IC. There is also an issue with the tightened fasteners and the tie-down force exerted by the spring.
What is desired is a self-aligning nut-type structure for use with board mounted studs for securing a heat sink to an IC chip.
What is also desired is to provide this nut structure captivated to the heat sink base.
What is further desired is to provide this nut structure with a spring tie-down, whereof the nut can float on the heat sink base and the spring exerts the tie-down force,
What is also further desired is to provide this nut structure with a positive adjustment for setting the spring force to a consistent predetermined spring force.